Andoid之硬件访问服务1（让Andoid应用程序访问c库）

andoid 项目文件结构图

新建Hardcontrol.java

package com.thisway.hardlibrary;

public class HardControl {
    public static native int ledCtrl(int which, int status);
    public static native int ledOpen();
    public static native void ledClose();

    static {
        try {
            System.loadLibrary("hardcontrol");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

访问C库

　　1.修改build.gradle

sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }

　　新建hardcontrol.c文件

#include <jni.h>    /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */
#include <stdio.h>
#include <stdlib.h>

#include <android/log.h>  /* android log*/

#if 0
 typedef struct {
    char *name;          /* Java里调用的函数名 */
    char *signature;    /* JNI字段描述符, 用来表示Java里调用的函数的参数和返回值类型 */
    void *fnPtr;          /* C语言实现的本地函数 */
} JNINativeMethod;
#endif

jint ledOpen(JNIEnv *env, jclass cls)
{   __android_log_print(ANDROID_LOG_DEBUG, "JNIDemo", "native add ...");
    __android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledOpen......");
    return ;
}

void ledClose(JNIEnv *env, jclass cls)
{
    __android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledClose......");
}

jint ledCtrl(JNIEnv *env, jclass cls,jint which, jint status)
{
    __android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledCtrl: %d,  %d",which, status);

    return ;
}

static const JNINativeMethod methods[] = {
    {"ledOpen", "()I", (void *)ledOpen},
    {"ledClose", "()V", (void *)ledClose},
    {"ledCtrl", "(II)I", (void *)ledCtrl},
};

/* System.loadLibrary */
JNIEXPORT jint JNICALL
JNI_OnLoad(JavaVM *jvm, void *reserved)
{
    JNIEnv *env;
    jclass cls;

    if ((*jvm)->GetEnv(jvm, (void **)&env, JNI_VERSION_1_4)) {
        return JNI_ERR; /* JNI version not supported */
    }
    cls = (*env)->FindClass(env, "com/thisway/hardlibrary/HardControl");
    if (cls == NULL) {
        return JNI_ERR;
    }

    /* 2. map hello java<-->c c_hello */
    if((*env)->RegisterNatives(env, cls, methods, sizeof(methods) / sizeof(methods[])) < )
        return JNI_ERR;

    return JNI_VERSION_1_4;
}

　　2.编译so文件

arm-linux-gcc -fPIC -shared hardcontrol.c -o libhardcontrol.so 
-I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/  
-nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so 
-I /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/include 
/work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/liblog.so

　　3.在app/libs下建armeabi子目录，放入so文件

　在4412开发板上运行，点相应按钮后会有调试信息打印